1. Field of the Invention
The present invention relates to a sliding type, tripod type constant velocity universal joint.
Generally, a constant velocity universal joint is a kind of universal joint that establishes connection between a driving shaft and a driven shaft to allow torque transfer with constant velocity regardless of the angle between the two shafts. In a sliding type, joint plunging permits relative axial displacements between the two shafts. In a tripod type, a tripod member having three radially-projecting trunnions is linked to one of the shafts, and a hollow, cylindrical outer joint member having three axially-extending track grooves is linked to the other, so that the track grooves in the outer joint member accommodate the trunnions of the tripod member for torque transfer.
2. Description of the Related Art
Now, referring to FIGS. 10(A) to 10(C), description will be given of a sliding type, tripod type constant velocity universal joint. In this universal joint, an outer joint member 1 has three cylindrical track grooves 2 axially formed in its inner periphery. A tripod member 4 inserted into the outer joint member 1 has three radially-projecting trunnions 5. Each of the trunnions 5 has a cylindrical outer periphery on which an annular roller 7 is rotatably fitted via a plurality of needle rollers 6. The rollers 7 are inserted into the track grooves 2. Each track groove 2 has a pair of circumferentially-opposed roller guideways 3 which are concave surfaces axially parallel to each other. Each of the rollers 7 on the three trunnions 5 has an outer periphery of convex surface conforming to the roller guideways 3. Each roller 7 can move along the corresponding track groove 2 while engaging with the roller guideways 3 of the track groove 2 to rotate about the trunnion 5.
When the joint transfers torque with an operating angle of xcex8 as shown in FIG. 10(B), the rollers 7 and the roller guideways 3 are put in an oblique relationship as shown in FIG. 10(C). In this case, the roller 7 tries to roll in the direction shown by the arrow t in FIG. 10(B). However, since the track groove 2 is part of a cylindrical surface parallel to the axis of the outer joint member, the roller 7 is confined to move along the track groove 2. As a result, the roller guideway 3 and the roller 7 cause a slide therebetween, producing a slide resistance. This slide also leads to an inductive thrust in the axial direction. Such slide resistances and inductive thrusts contribute to the production of vibrations and noises from a car body, affecting the noise vibration harshness (NVH) performances of motor vehicles and decreasing the flexibility in automotive suspension design. Thus, the resistances and thrusts are desirably reduced as much as possible.
Sliding type, tripod type constant velocity universal joints known as contemplated to reduce such slide resistances and inductive thrusts include the one having the structure shown in FIGS. 11(A) to 11(C). Specifically, as shown in the figures, each trunnion 5 of the tripod member 4 has an outer periphery of perfect spherical surface. To the perfect spherical surface is slidably fitted on the cylindrical inner periphery of a cylindrical ring 8. Each ring 8 and roller 7 constitutes a roller assembly capable of relative rotations therebetween through the medium of rolling elements. Needle rollers 6, the rolling elements, are arranged between the cylindrical outer periphery of the ring 8 and the cylindrical inner periphery of the roller 7 to provide a so-called full complement type bearing. The needle rollers 6 are stopped by annular washers 9. The rollers 7 are accommodated in the track grooves 2 of the outer joint member 1 so as to move along the axial directions of the outer joint member 1 while rolling on the roller guideways 3 in the track grooves 2.
The outer periphery of each trunnion 5 is a perfect spherical surface having the center of curvature on the axis of the trunnion 5. The roller assembly (7, 8) nutates about the center of curvature. Due to the roller assembly""s capability of nutation, when the outer joint member 1 and the tripod member 4 perform torque transfer with an operating angle, the rollers 7 are guided by the roller guideways 3 of the outer joint member 1 so as to remain parallel to the axis of the outer joint member 1 while properly rolling on the roller guideways 3 in the same orientations. This reduces slides during the operation with angles, thereby suppressing the production of slide resistances and inductive thrusts.
Sliding type, tripod type constant velocity universal joints are known as being used for constant-velocity torque transfer from the engine to wheels of a motor vehicle. In a sliding type, tripod type constant velocity universal joint, spherical rollers are mounted on the trunnions of its tripod member. Between the outer peripheries of the trunnions and the inner peripheries of the spherical rollers are arranged needle rollers as rolling elements. The needle rollers are used as full complement type bearings without retainers. In transferring torque with an operating angle, internal components of the joint cause mutual frictions to generate inductive thrusts during rotations. Even at rest, forced extension or contraction of the joint produces slide resistances. Automotive NVH phenomena typically associated with such inductive thrusts and slide resistances include the rolling of a moving car and the vibrations of a car idling with its automatic transmission in a drive or D range, respectively.
The essence of the solution to the automotive NVH problems consists in reducing inductive thrusts and slide resistances a joint can produce. In general, inductive thrusts and slide resistances from a joint tend to depend upon the operating angle of the joint. In applications to automotive drive shafts, this tendency leads to a design limitation of prohibiting greater operating angles. Accordingly, the challenge to an improvement in flexibility of automotive suspension design is to reduce and stabilize the inductive thrusts and slide resistances.
In view of the foregoing, it is an object of the present invention to further reduce and stabilize such inductive thrusts and slide resistances.
According to an embodiment of the invention, a constant velocity universal joint comprises: an outer joint member having three track grooves each having circumferentially-opposed roller guideways; a tripod member having three radially-projecting trunnions; a roller inserted in each of the track grooves; and a ring fitted on each of the trunnions to support the roller rotatably, the roller being movable in axial directions of the outer joint member along the roller guideways. Here, the inner periphery of the ring is shaped arcuate and convex insection. The outer periphery of each of the trunnions is shaped straight in longitudinal section, as well as formed in cross section so as to make a contact with the inner periphery of the ring along a direction perpendicular to the axis of the joint and create a clearance with the inner periphery of the ring in an axial direction of the joint.
The cross-sectional configuration of the trunnions so as to make a contact with the inner periphery of the ring along a direction perpendicular to the axis of the joint and create a clearance with the inner periphery of the ring in an axial direction of the joint may otherwise be put in the following words. That is, the faces opposed to each other in the axial direction of the tripod member have made a retreat toward each other, i.e., to smaller diameters than the diameter of the imaginary cylindrical surface. A concrete example of such configuration is an ellipse.
Due to the alteration in cross section from the conventional circular shape to the configuration described above, the trunnions can tilt with respect to the outer joint member without changing the orientations of the roller assemblies when the joint operates with an operating angle. Besides, as is apparent from a comparison of FIG. 1(C) with FIG. 11(C), the osculating ellipses of the rings with the outer peripheries of the trunnions approach from oblong ellipses to points in shape. This reduces the friction moments functioning to tilt the roller assemblies. As a result, the orientation of the roller assemblies is stabilized, so that the rollers are maintained parallel to the roller guideways for smooth rolling. This smooth rolling contributes to reduced slide resistances and, finally, to reduced inductive thrusts. Moreover, there is an advantage that the trunnions improve in flexural strength because of an increase in the section modulus at the bottom portions of the trunnions.
The roller assemblies are to be interposed between the trunnions and the outer joint member for the sake of torque transfer. In a constant velocity universal joint of this type, the transfer direction of torque is always perpendicular to the axis of the joint. Thus, as long as they contact in the transfer direction of the torque, the trunnions and the rings can perform torque transfer without trouble even when they have clearances therebetween in the axial directions of the joint.
The trunnions maybe formed to have a cross section of generally elliptic configuration with the major axis perpendicular to the axis of the joint. The generally elliptic configuration is not literally limited to perfect ellipses, and may include those generally referred to as ovals and suchlike. More specifically, the trunnions can adopt such cross-sectional configurations as to relax contact pressures against the rings and avoid a drop in strengths of trunnions. Besides, the trunnions can tilt without inclining the rings, which prevents the rollers from inclination and allows the rollers to roll smoothly on the roller guideways. As a result, it becomes possible to omit ribs which sometimes are arranged on the track grooves in the outer joint member with an aim to restrain the inclination of the rollers. The omission of the ribs not only reduces the outer joint member in weight and simplifies the machining thereto, but eliminates slide resistances that result from the slide contacts between the rollers and the ribs. This achieves a further reduction in slide resistance and inductive thrust.
The outer periphery of each trunnion and the inner periphery of the ring may advantageously create a clearance of 0.001a or more therebetween in a circumferential direction of the joint, where a is the semi major axis of the generally elliptic cross section of the trunnion. Such clearances can well absorb the tilt of the trunnions resulting from the revolutions of the trunnion center, which is peculiar to tripod type constant velocity universal joints. This absorption removes the factors responsible for the inclinations of the roller assemblies within the joint""s cross section, contributing to improved NVH performances of motor vehicles.
The generator to the inner periphery of the ring may be composed of an arc portion at the center and relief portions on both sides. The radius of curvature at the arc portion favorably has a value that allows the trunnions to make a lean of the order of 2-3xc2x0.
A plurality of rolling elements are arranged between the ring and the roller to allow relative rotations between the ring and the roller. Aside from cylindrical rollers such as needle rollers, the rolling elements maybe balls as well. Here, the contact between the trunnion and the inner periphery of the ring always stays at the lateral center of the ring, thereby ensuring the stable rolling of the rolling elements. Besides, the centers of the inner peripheral surface of the ring and of the outer peripheral surface of the roller are on substantially the same level, which ensures that the roller assembly remains steady without tilting.
The outer periphery of the roller may be formed in a spherical form to make an angular contact with the roller guideways in the outer joint member. The angular contacts between the roller and the roller guideways make the roller less prone to vibrate, stabilizing the orientation of the roller. As a result, the roller can roll on the roller guideways with smaller resistances when moving along the axial direction of the outer joint member. The specific cross-sectional configurations for the roller guideways to establish such angular contacts include a tapered and a Gothic arc shape.
Grinding may be applied to the outer periphery of each of the trunnions, exclusively at a prescribed area including the contact area to the inner periphery of the ring. In consideration of machining errors and the like, the prescribed area is favorably determined to be somewhat wider than the contact area. The remaining area other than the prescribed area may be left forge-finished without any grinding. This allows a cut in machining time and a reduction in cost.
The present invention provides a constant velocity universal joint comprising: an outer joint member having three track grooves each having circumferentially-opposed roller guideways; a tripod member having three radially-projecting trunnions; a roller inserted in each of the track grooves; and a ring fitted on each of the trunnions to support the roller rotatably, the roller being movable in axial directions of the outer joint member along the roller guideways. Here, the inner periphery of the ring is shaped arcuate and convex in section. The outer periphery of each of the trunnions is shaped straight in longitudinal section, as well as formed in cross section so as to make contact with the inner periphery of the ring along a direction perpendicular to the axis of the joint and create a clearance with the inner periphery of the ring in an axial direction of the joint. Accordingly, when the joint operates with an operating angle, the trunnions can tilt with respect to the outer joint member without ever changing the orientations of the roller assemblies. Besides, the osculating ellipse between the outer periphery of each trunnion and the ring approaches from an oblong ellipse to a point in shape. This change in shape reduces the friction moment functioning to tilt the roller assembly. In addition, the contacts between the trunnions and the rings"" inner peripheries always stay at the lateral centers of the rings. Therefore, even when rolling elements such as needle rollers are arranged between the rings and the rollers, the undeviating contacts ensure the stable rolling of the rolling elements. As a result, the orientations of the roller assemblies are stabilized consistently, so that the rollers can be maintained parallel to the roller guideways to roll smoothly. This smooth rolling contributes to reduced slide resistances and reduced inductive thrusts as well. Moreover, there is an advantage that the trunnions are improved in flexural strength because of an increase in the section modulus at the bottom portions of the trunnions.
The nature, principle, and utility of the invention will become more apparent from the following detailed description in conjunction with the accompanying drawings in which like parts are designated by like reference numerals or characters.